1. Field of the Invention
The present invention is directed toward a hopper car gate assembly and, more particularly, to a hopper car gate assembly with a door having vertically spaced sections.
2. Description of Related Art
Sand used in hydraulic fracturing is commonly transported in a hopper railcar having at least one gravity discharge gate assembly for unloading the sand. When the hopper car reaches its destination, the sand is typically unloaded with a conveyor that extends underneath the hopper car's gate assembly. For the conveyor to fit underneath the gate assembly, there must be a sufficient amount of clearance between the bottom of the gate assembly and the rails over which the hopper car travels.
Hydraulic fracturing sand is commonly transported in a type of hopper railcar that is commonly referred to as a cement car because the car is well adapted for transporting cement. Further, a particular type of gate assembly that is commonly referred to as a cement gate assembly is mounted to the bottom of a cement car to discharge the cargo within the car. A cement gate assembly typically has a top opening that is sized to correspond with the opening in the bottom of a cement car. Further, a cement gate assembly typically has a bottom opening that is sized to correspond with the opening in a cement boot, which is a device that is positioned adjacent to a cement gate assembly during unloading to receive cargo discharged through the gate assembly. A conventional cement car having a conventional cement gate assembly is not typically suitable for hauling hydraulic fracturing sand because the sand unloading conveyor does not fit between the bottom of the gate assembly and the rails over which the car travels.
Two gate assemblies have been developed that mount to the bottom of a conventional cement car and provide the necessary clearance for unloading with a sand conveyor. The first type of gate assembly is similar to a conventional cement gate assembly except that a hopper of the gate assembly is shallower than the hopper of a conventional cement gate assembly so that there is sufficient clearance beneath the gate assembly for unloading with a sand conveyor. The gate assembly has a top opening that is the same as the top opening of a conventional cement gate assembly, and the hopper walls of the gate assembly are angled in the same manner as the hopper walls of a conventional cement gate assembly. Because the gate assembly's hopper is shallower than the hopper of a conventional cement gate assembly and the gate assembly's hopper walls are angled in the same manner as the hopper walls of a conventional cement gate assembly, the bottom opening of the gate assembly is larger than the bottom opening of a conventional cement gate assembly. Because the gate assembly has a larger bottom opening, cargo cannot be unloaded with a conventional cement boot having an opening that is sized to correspond with the smaller bottom opening of a conventional cement gate assembly. Thus, while this first type of gate assembly may be used with a sand unloading conveyor, it is not suitable for use with a hopper car transporting cement.
The second type of gate assembly that provides the necessary clearance for unloading with a sand conveyor is similar to the first type of gate assembly described above, except that the second type of gate assembly includes a structure positioned below the gate assembly's door which is sized so that the gate assembly can mate with and discharge cargo into a conventional cement boot. The structure mounts on or is integral with the gate assembly's frame and includes a top opening that receives cargo passing through the gate assembly's door and a bottom opening that is sized to correspond with the size of a conventional cement unloading boot. The height of the structure is such that there is sufficient clearance for a sand unloading conveyor to fit beneath the gate assembly. While this gate assembly may be unloaded with both a conventional cement boot and a sand conveyor, cargo passing through the gate assembly can accumulate on the structure beneath the door and interfere with the gate assembly's operation.